[BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread

[Mbradford6288]

So, I got a pair of red dots, and now the pre seems to be working.  Except no LEDs work.  I get signal.  But no light show.  I put in the gar2520s I built, and lights, but no signal. 

Has anybody experienced this?  Any thoughts?

 

[kante1603]

So, I got a pair of red dots, and now the pre seems to be working.  Except no LEDs work.  I get signal.  But no light show.  I put in the gar2520s I built, and lights, but no signal. 

Has anybody experienced this?  Any thoughts?

Hello,


seems you have multiple errors in your build.
So let's start with the audio first.You say "now the pre seems to be working".From your previous posts I can see you have tested GAR2520 and 990s.Did you build them yourself?
With red dots it seems to work you say,We must have this confirmed first to get it all started.
So please check this first,do a unity gain check.If it is o.k. check all switches for functionality,then the gain and fader positions.What do you get?


For leds not working,it's seems you might have one or some reversed.
For input led not working,might be a) led reversed,b) 4558 chip reversed,c)both.
Once the chip was reversed and powered up and will be dead forever.


But first do the audio stuff and stick with the red dots.


Best regards and good luck,


Udo.

 

[Mbradford6288]

Hey Udo,

Thanks for the response.  Definitely multiple errors.  :-[

All sonic functions are working correctly with the red dots.  Phase, mic/line, phantom, and the pad.  Hpf works.  Gain and output fader are operating correctly.  Unity is correct.  Signal is clean and fat and beautiful. 

No lights. 

When I put in the gars, all lights work properly.  No sound. 
I've double checked all the leds, they are in properly, although green was backwards initially, providing a constant beautiful green glow.  Now it's in th right way.  No love.

Ic and oc socket are in properly.  Double checked. 

My red dots only have 5 pins, no pin for common, which I assume is normal. 

Obviously my build on one of the gars was not right, but lights still come on with gars, but no sound.  Killer sound with red dots, no lights. 

Thanks for any thoughts or help. 

 

[Unit7]

I've double checked all the leds, they are in properly, although green was backwards initially, providing a constant beautiful green glow.  Now it's in th right way.  No love.

Obviously my build on one of the gars was not right, but lights still come on with gars, but no sound.  Killer sound with red dots, no lights. 

Not my intention to be Mr Obvious, but some things in your post makes me just want to check that you know that the signal led only should light up when the unit gets a signal strong enough.

 

[kante1603]

Not my intention to be Mr Obvious, but some things in your post makes me just want to check that you know that the signal led only should light up when the unit gets a signal strong enough.

Good point (Hi Paul ).
I'm also confused about the other leds which just indicate the status of the switches,so not signal related at all.
Just to sum it up:The status leds work with GARs but not with red dots???
From what I understood this is just a led series-string.....how can a doa make them misbehave except of causing a short which will end up in a blown fuse in the psu?
The signal led is a different thing driven by the 4558.....


Strange.......


Udo.

 

[Mbradford6288]

No problem with the obvious thing.  I am aware the green should only light up when signal is strong enough.  I just meant to say I know the green LED is able to work because I've seen it on, but no signal light at all.  Thanks Paul. 

Yes udo, none of the status lights work with the Red Dots.  When I put the gars in, they all function correctly. 

Everything sounds great, and I figure I screwed up one of my gars because I'm getting good signal with the Red Dots.  Still no lights though, including the signal LED, when I'm feeding a signal. 

 

 

[kante1603]

o.K.,we must ask Jeff then,I'm running out of ideas atm.
Still completely weird to me because I really wonder how different doas can affect even the status leds.
I wonder what would happen if the working GAR2520 is inserted together with one of the red dots......
You said you have messed up only one of them,so why not try it.......


Best,


Udo.

 

[Mbradford6288]

Alright, so, now it's extra weird.

Udo, thanks for that very logical problem solving solution.  It makes complete sense, which is why I never thought of it.

I have two Gars that I built. 

One of the gars passes signal, and I get good sound.  No LED function.  That occurs in either opamp position. 

The other gar, I get no sound, but LEDs function properly.  That also occurs in either opamp position. 

 

[MattRoss]

Hi Guys,

It wasn't till I built my second VP28 that I realized something was definitely wrong with the first one. The first one has gotten worse for wear over the past year, it didn't always sound quite this bad, but I'm wondering if you guys can help identify the issue. I've linked to a recording of the 2 VP28s back to back, the healthy one, then the troubled one.

The only functions engaged in both are the phantom power and mic button, no HP on either. The HP does work, further thinning the sound. Both 28's use red dots op amps.

AA-CM47 > VP28 (A/B) > Duet XLR Line +4dBu > Pro Tools.

I've already reflowed solder and checked just about every joint I can find. The troubled VP28 only operates with the gain pushed to maximum, before that there is no signal recognition whatsoever.

I appreciate any feedback!

https://soundcloud.com/ross-matthei/vp28-the-good-the-bad

 

[jswagler55]

Matt this is strange because as of yesterday one of my vp28s is doing the same exact thing as yours.  I just recorded a sample if i needed it and sounds just like yours with the gain and fader maxed out.

Only with mine it  really hasn't shown any issues till now. I have 5 vp28s and all have been build for about 6 months or longer with no real issues till now.  Mine has worked randomly for about 10 seconds and then goes back to the distorted / high pass filter kind of sound. I switched out op-amps with another one and that wasn't the problem. Switched slots on the power supply nothing different. Looked over soldering nothing looked suspicious. 

The signal light does look like its functioning normally which leads me to believe its something on the output.

 

[MattRoss]

Yes, the signal indicator is working fine and op amps have been switched. I have one flipped resistor, is that a necessary fix? It's my understanding they're not polarized other than for identification purposes.

 

[Mbradford6288]

Why are resistors rf5, 6, and 7 not in ascending order of resistance on the output fader when all the rest are?  At this point, just a random question as a double and triple check everything.

Thanks!

Matt

 

[Mbradford6288]

I've triple checked everything. 

Same deal as before. 

One of my Gars works for sound, one allows the LEDs to work.  No love at all from the signal LED.  Red dots great sound, no LEDs. 

It appears line level, when I ran it again, is actually 8 db above unity.  Tried it the first time on a buddy's interface and may have just had it set wrong.  Double checked it in my studio, controlled environment, and I have unity at the -8 channel fader setting, with the preamp gain set at line unity gain.

I've triple checked all resistors, and most of the caps.  All of the transformer wires.  I resoldered the LEDs.  Replaced C8, Radial electrolytic because the original appeared to be bulging slightly on the top. 

One odd thing, it appears I have no resistance between lugs 1-4, and no resistance between lugs 5-8 on the input transformer.  Couldn't find a schematic of the circuit.  Is that right?  Or did I potentially catch the housing with solder?  I tried to pull it, but I don't have the right tools I don't think.  :-[

Thanks for any advice.  Frankly, it's working and sounds pretty great.  I'd like to get a second to have a stereo set, but I can't pull the trigger until I have this one cranking right. 

 

[frenkonio]

Hi all!
I built some VP28 till now. Latest stereo pair I've assembled showed different values on my DMM. One VP28 A3 gives me (on 0/+V) a value of 13.95V, instead of A1 giving 14.99V.  The second VP28 gives (on 0/+V) a value of 14.95 on both A1 and A3.
I thought: damn, something is not right. So I inserted a GAR1731 and a GAR2520 (pre tested) on both VP28 and put them inside the 500 series rack (a Lindell Audio unit). I used both mic and line signals and.. both worked perfectly, no discrepancy in the stereo image at every step of both input & output fader. Every switches, led work. I have tried to put a sine wave at 1Khz and the result was equal on both channel.
Why is it possible if the DOA values on the DMM were different and a bit distant from the normal 16V?!
Thanks for the help & infos you'll give me!

 

[jswagler55]

Yes, the signal indicator is working fine and op amps have been switched. I have one flipped resistor, is that a necessary fix? It's my understanding they're not polarized other than for identification purposes.

Matt did you reheat any of the HPF board cause I believe that is where my problem was. I did the rest of the board and nothing changed, then I reheated some of the pins on the HPF board and everything works again.

 

[MattRoss]

That did it

 

[Fenix511]

Ok question for capacitors C1 and C12. My kit came with a 330uf 16v instead of 330uf 25v for C1 and 1uf 63v instead of 1uf 100v for C12. I assume it is fine but since the values are different then the BOM I wanted to be sure. Thank you for your time.

 

[jsteiger]

Ok question for capacitors C1 and C12. My kit came with a 330uf 16v instead of 330uf 25v for C1 and 1uf 63v instead of 1uf 100v for C12. I assume it is fine but since the values are different then the BOM I wanted to be sure. Thank you for your time.

Yes this is fine. I changed the 330uF to 16V since it should never see more than 100mV or so of DC.

Vishay/BC discontinued the 1uF/100V that is white and looks like the 33uF so I had to use the closest substitution from them. I have not been able to hear a dif but the other ones are unobtainium so sadly this is how we will move forward. This cap should also never see more than 100mV DC so the voltage rating here doesn't really matter.

 

[Fenix511]

Thank you for that speedy replay I finished up them and honestly they are even better then I expected and I already had 2 VP25 pres. Now I just gotta get some more money to get some more rack space.

 

[Commander Fluffypants]

Hi folks,

I have six VP28's, five of which work very well. The other one has some strange symptoms. I believe this is the one I posted about a while back. (Due to life situations and an historically hellish winter here, I've hardly done any recording at my studio, and no full band stuff where I'd need all my inputs, until now when I'm noticing this issue.)

First thing I did was swap out my DOA's with ones from a working unit, so I know it's not theDOA's. Too bad. That would be an easy fix. The symptoms are a HUGE pop when engaging the pad, a huge pop when engaging the phantom and a bit of a pop when engaging the mic/line switch. Phase button makes no pop. If that was it, I could live with it, but none of my other units make these noises and more important, there is a bit of hiss and hum in this one and possibly some signal distortion. It's not that loud, but it is audible, especially at high gain. Both knobs affect the volume of the noise(s). None of my other VP28's make these noises. As far as I can tell, everything is in correctly.

Any ideas?

Thanks, as always!